In general, a photoconduction process which utilizes an electrophotographic light-sensitive material, comprises the steps of:
(1) generating electric charges by light-exposure; and PA1 (2) transporting the electric charges. PA1 (1) It can be charged at a suitable potential in a dark place; PA1 (2) Little or no dissipation of electric charges occurs in a dark place; and PA1 (3) Irradiation with light permits rapid dissipation of electric charges. PA1 (ii) R.sup.1 and R.sup.5 may be the same or different, and are each a hydrogen atom, an alkyl group, an aralkyl group, an aryl group or heterocyclic group; PA1 (iii) A.sup.1 is a univalent group derived from a substituted phenyl group, a monocyclic or condensed 5-membered heterocyclic ring, or a condensed 6-membered heterocyclic ring represented by the following general formulae: ##STR3## wherein R.sup.6 is an alkoxy group, an aralkyloxy group or a substituted amino group represented by the formula: ##STR4## (wherein R.sup.12 and R.sup.13 may be the same or different, and are each a substituted or unsubstituted alkyl group, or a substituted or unsubstituted phenyl group, or they are groups capable of combining together to form a nitrogen-containing heterocyclic ring; R.sup.7 and R.sup.8 may be the same or different, and are each a hydrogen atom, a halogen atom, an alkyl group or a lower alkyl group; Y and Z may be the same or different, and are each a sulfur atom (S), an oxygen (O) or a group N-R.sup.14 (wherein R.sup.14 is an alkyl group containing 1 to 4 carbon atoms); R.sup.9 and R.sup.10 may be the same or different, and are each a hydrogen atom, an alkyl group or an alkoxy group, or they are groups capable of combining together to form a benzene ring or naphthalene ring; and R.sup.11 is a hydrogen atom, an alkyl group, an alkoxy group, an aryloxy group, an acryl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a halogen atom, a monoalkylamino group, a dialkylamino group, an amido group or a nitro group, which may be either substituted or not substituted; PA1 (iv) A.sup.2 is a divalent group derived from a heterocyclic ring nucleus selected from the group consisting of imidazole, 3H-indole, thiazole, benzothiazole, naphthothiazole, thianaphtheno-7', 6',4,5-thiazole, oxazole, benzooxazole, naphthooxazole, seneazole, benzoselenazole, naphthoselenazole, thiazoline, 2-quinoline, 4-quinoline, 1-isoquinoline, benzimidazole, 2-pyridine, and 4-pyridine; and PA1 (V) B is a group of atoms required for forming a divalent group which is derived from a carbon ring or heterocyclic ring containing the oxo oxygen atom of the carbonyl group linked to a ring represented by the formula: ##STR5## wherein W is O, S or SO.sub.2 ; R.sup.15 is the same as defined for R.sup.11 ; R.sup.16 is an alkyl group, an aralkyl group, or an unsubstituted or substituted aryl group; and R.sup.17 and R.sup.18 may be the same or different, and are each an alkyl group, an aralkyl group or an unsubstituted or substituted phenyl group.
Light-sensitive materials can be divided into a group in which the steps (1) and (2) above are performed by the same substance, and a group in which they are performed by different substances. A typical example of the former group is a selenium light-sensitive material. For the latter group, a combination of amorphous selenium and poly-N-vinyl carbazole is well known. Light-sensitive materials falling within the latter group have advantages in that a wide range of starting materials can be used in the preparation of the light-sensitive materials. This may make it possible to increase electrophotographic characteristics such as the sensitivity of light-sensitive material and receiving potential, and in that substances suitable for increasing these characteristics can be chosen from a wide range.
Photoconductive materials which have heretofore been used in light-sensitive materials to be used according to the electrophotographic system include inorganic substances such as selenium, cadmium sulfide, and zinc oxide.
The electrophotographic process disclosed by Carlson in U.S. Pat. No. 2,297,691, uses a photoconductive material comprising a support coated with a substance which is insulative in a dark place and changes its electric resistance depending on the amount of light irradiated during imagewise exposure. In general, the photo-conductive material, after being subjected to dark conditioning for a suitable period of time, is uniformly provided with electric charges on the surface thereof in a dark place. Thereafter, the material is exposed imagewise according to a pattern of irradiation having the effect of reducing surface electric charges depending on the relative energy contained in various parts of the pattern. The surface electric charges thus allowed to remain on the photoconductive substance layer (light-sensitive layer), i.e., an electrostatic latent image, is converted into a visible image by bringing the photoconductive substance layer into contact with suitable detection-indicating substances, i.e., toners.
These toners can be drawn to the surface of the light-sensitive layer according to an electric charge pattern even though they are contained in an insulative liquid or in dry carriers. The thus-drawn toners can be fixed by known techniques such as application of heat, pressure of solvent vapor. Furthermore, the electrostatic latent image can be transferred to a second support. Similarly, the electrostatic latent image can be transferred to a second support (e.g,, paper and a film) where it is developed.
Some of the fundamental characteristics required for the light-sensitive material for use in the electrophotographic process are:
The above described inorganic substances which have heretofore been used as photoconductive materials suffer from various disadvantages although they have many advantages. For example, selenium that is presently in widespread use sufficiently meets the above requirements (1) to (3). However, use of this material is not desirable because production conditions are severe, production costs are high, flexibility is poor, it is difficult to shape into a belt-like form. Furthermore, care must be taken in handling since it is of low resistance against heat or mechanical impact. Cadmium sulfide and zinc oxide are used as light-sensitive materials in which they are dispersed in resins as binders. However, they cannot be used repeatedly as such since they are inferior in mechanical properties such as smoothness, hardness, tensile strength, and frictional resistance.
In recent years, to remove the above described defects of the inorganic substances, electrophotographic light-sensitive materials prepared using various organic substances have been proposed, and some of the light-sensitive materials have been put into practical use. Examples include a light-sensitive material containing poly-N-vinyl carbazole and 2,4,7-trinitrofluorene-9-on as described in U.S. Pat. No. 3,484,237, a light-sensitive material containing poly-N-vinyl carbazole which is sensitized with pyrylium salt-based dye, as described in Japanese Patent Publication No. 25658/73, a light-sensitive material containing organic pigment as a major component as described in Japanese Patent Application (OPI) No. 37543/72 (the term "OPI" is used herein to refer to a "published unexamined Japanese Patent application), and a light-sensitive material containing an eutectic complex of a dye and a resin, as described in Japanese Patent Application (OPI) No. 10735/72. These light-sensitive materials are believed to have excellent characteristics and to be of high practical value. In practice, however, no light-sensitive material sufficiently satisfies all the requirements for a light-sensitive material, e.g., convenient to produce, exhibits satisfactory electrophotographic characteristics, and a good wavelength selectivity which is required when the light-sensitive material is used as a laser beam printer or an indication element.
As a result of extensive study on charge-generating materials, it has been found that the compounds represented by the general formula (I) or (II) as defined hereinafter exhibits excellent performance as charge-generating materials, and sufficiently satisfy the requirements for light-sensitive materials.
Merocyanine dyes are known as spectral sensitizing dyes for silver salt photographs, and have been extensively studied in that field. In recent years, an attempt to use these cyanine dyes in light-sensitive materials for electrophotography, particularly as electrically light-sensitive particles for use in the electrophoretic image-forming process has been made, but they do not exhibit satisfactory characteristics.
It has been found that the compounds represented by the general formula (I) or (II) as defined hereinafter have excellent charge-generating capability. Furthermore, the electrophotographic light-sensitive materials prepared using the compounds as charge-generating materials in combination with charge-transporting materials are of very high sensitivity and are convenient to produce. These materials have good durability and exhibit sufficiently satisfactory electrophotographic characteristics.
Furthermore, it has been found that the electrophotographic light-sensitive materials have good wavelength selectivity which is required when they are used as laser beam printers or indicating elements. In addition, the compounds of the invention can be uniformly dispersed as charge-generating materials together with charge-transporting materials. They may be advantageous toward obtaining light-sensitive materials of high transparency.